1. Field of the Invention
The present invention relates to a process for melt-bonding a molded article of a thermotropic liquid crystalline polyester resin with a metal and a process for producing a molded article formed from a molded article of a thermotropic liquid crystalline polyester resin and a metal.
2. Description of the Related Art
Since thermotropic liquid crystalline polyester resins (hereinafter, sometimes may be referred to as liquid crystalline polymers) have characteristics that they are superior in heat resistance and excellent in flowability at a molten state, they have become widely used centering around the field of electronic materials as injection molding materials usable in high precision molding. One of use thereof in which their heat resistance and lower linear thermal expansion, parts of their excellent characteristics, are made good use is a product for use as mechanical parts, electric parts and electronic parts produced by plating or adhering a metal on a surface of a part molded by injection molding or a film molded by extrusion molding.
In these parts, the molded article and the metal must be adhered with a sufficient strength for practical use. The molded articles of a thermotropic liquid crystalline polyester resin, however, have a weak contact ability because of strong molecular orientation on the surface of molded article and are inactive to almost all chemicals. Therefore, sometimes a sufficient adhesive strength can not be obtained upon adhesion or plating.
Thus, various processes have been attempted for improving adhesive strength between molded articles of a thermotropic liquid crystalline polyester resin and metals. For example, JP-A-1-216824 discloses, as a method for modifying a surface of a molded article of a thermotropic liquid crystalline polyester, a process for obtaining a surface suitable for painting, printing, adhesion, deposition, plating and so on by irradiating with ultraviolet rays. In addition, JP-A-9-100359 discloses a process for obtaining a surface of a molded article excellent in adhesive strength upon plating or others by partially irradiating a surface of a molded article of a thermotropic liquid crystalline polyester resin with ultraviolet rays and then roughening the surface with an etching solution.
When, however, a thermotropic liquid crystalline polyester resin is adhered to a metal by an adhesive, the property of the adhered molded article is strongly damaged due to an inferior property of the adhesive, although the thermotropic liquid crystalline polyester resin is excellent in properties such as heat resistance and dielectric property. In addition, plating requires troublesome steps such as etching.
On the other hand, various processes have been attempted in which a metal and a thermotropic liquid crystalline polyester resin are melt-bonded rather than adhering or plating. In one example, JP-A-8-58024 discloses a process for obtaining a laminate useful as a substrate for circuit by melt-bonding a film of thermotropic liquid crystalline polyester resin with a copper foil.
Even such a product obtained by a process in which a molded article of thermotropic liquid crystalline polyester resin is melt-bonded with a metal has sometimes not a sufficient adhesive strength between the liquid crystalline polyester resin and the metal.
The object of the present invention is to provide a process for melt-bonding a molded article of a thermotropic liquid crystalline polyester resin with a metal with firmness and a process for producing a laminated product in which a molded article of a thermotropic liquid crystalline polyester resin molded article and a metal is laminated with firmness.
As the result of extensive studies for resolving the above problems, the present inventors have found that the above object can be attained by previously activating a surface of a molded article of a thermotropic liquid crystalline polyester resin and melt-bonding said surface with a metal at or above the flow temperature of said thermotropic liquid crystalline polyester resin. Thus, they have completed the present invention.
The present invention relates to (1) a process for melt-bonding a molded article of a thermotropic liquid crystalline polyester with a metal which comprises activating a surface of a molded article of a thermotropic liquid crystalline polyester resin and melt-bonding said surface with a metal at or above the flow temperature of said thermotropic liquid crystalline polyester resin.
Also, the present invention relates to (2) a process for melt-bonding a molded article of a thermotropic liquid crystalline polyester with a metal which comprises previously irradiating a surface of a molded article of a thermotropic liquid crystalline polyester resin with ultraviolet rays containing a wavelength 254 nm and melt-bonding said surface with a metal at or above the flow temperature of said thermotropic liquid crystalline polyester resin.
Further, the present invention relates to (3) a molded article comprising a molded article of a thermotropic liquid crystalline polyester and a metal, which is melt-bonded by the process according to above (1) or (2).
Still further, the present invention relates to (4) a process for producing a molded article formed from a molded article of a thermotropic liquid crystalline polyester and a metal which comprises, in a process for producing a molded article formed from a molded article of a thermotropic liquid crystalline polyester and a metal, previously irradiating a surface of a molded article of a thermotropic liquid crystalline polyester resin with ultraviolet rays containing a wavelength 254 nm and melt-bonding said surface with a metal at or above the flow temperature of said thermotropic liquid crystalline polyester resin.
Further, the present invention relates to (5) a process for producing a laminated product formed from a thermotropic liquid crystalline polyester and a metal which comprises, in a process for producing a laminated product formed from a molded article of a thermotropic liquid crystalline polyester and a metal, previously irradiating a surface of a molded article of a thermotropic liquid,crystalline polyester resin with ultraviolet rays containing a wavelength 254 nm and melt-bonding said surface with a metal at or above the flow temperature of said thermotropic liquid crystalline polyester resin.
The molded article of a thermotropic liquid crystalline polyester used in the present invention is a product molded from thermotropic liquid crystalline polyester resin by injection molding, extrusion molding or the like. Particularly, the molded articles in the form of films or sheet can be used as substrates for circuit excellent in heat resistance, dimension accuracy and the like by bonding together with a copper foil.
The thermotropic liquid crystalline polyester resin for obtaining such molded article can be obtained by polycondensation reaction with combining monomers of an aromatic hydroxyl carboxylic acid, an aromatic dicarboxylic acid and an aromatic dihydroxyl compound.
Examples of the aromatic hydroxyl carboxylic acid unit include: 
Examples of the aromatic dihydroxyl compound unit include: 
Examples of the aromatic dicarboxylic acid unit include: 
While combination and ratio of the monomer components may be determined according to desired object, it is preferred that the components represented by the following formulae (1), (2), (3) and (4) or formulae (1) and (5) are contained in an amount of 97% by mole or more, based on the total amount, for a liquid crystalline polyester having a high heat resistance and a suitable flowability. 
Among them, components represented by the formulae (1), (2), (3) and (4) are preferred for thermotropic liquid. crystalline polyester resin having a higher heat resistance. More preferred are those having the component represented by the formula (1) in an amount of 40 to 70% by mole based on the total amount, the amount of the components represented by the formula (2) plus formula (3) is 15 to 30% by mole based on the total amount, which is substantially the same as that for the component represented by the formula (4), and additionally, among the component (2), a proportion of a component in which the principal chains are bound in the para-position is 80 to 100% by mole based on the total component (2), and among the component (4), a proportion of a component in which the principal chains are bound in the para-position is 50% by mole or more based on the total component (4).
As a process for producing liquid crystalline polyester resin used in the molded article of the invention, any conventional processes can be used without particular limitation. For example, the resin can be obtained by carrying out a polycondensation reaction of a mixture comprising the above monomer compounds in a polymerization vessel. In this case, charging of the compounds may be in one portion or in divided portions. The reaction can be performed in an inert gas, for example under a nitrogen atmosphere, at the ordinary pressure or a reduced pressure, or a combination of them. For the process, a batch system, a continuous system or a combination of them may be adopted. In addition, the polycondensation reaction can be performed subsequent to a reaction (for example, esterification reaction) for converting the above monomer compound to a more easily polymerizing compound.
Preferred temperature for the polycondensation reaction is 270 to 380xc2x0 C. When the temperature is lower than 270xc2x0 C., the polymerization reaction is slow and when it is higher than 380xc2x0 C., side reactions tend to occur. Multiple step reaction temperature may be adopted. In some cases, it is also possible to take out and collect the polymer as the reaction product in a molten state in halfway of elevation of temperature or immediately after reaching to the maximum temperature. The collected polymer can be solidified and divided into powders or directly introduced from the polymerization vessel to an extruder and pelletized. Alternatively, the collected polymer can be subjected to a post-treatment such as solid phase polymerization by heating under a nitrogen atmosphere in order to increase further the molecular weight of the polymer.
It is preferred, for handling, that the obtained powders of liquid crystalline polymer are pelletized by an extruder and molded by an injection molding machine or an extrusion molding machine.
In addition, insofar as the object of the invention is adversely affected, various additives such as inorganic filler, organic filler, antioxidant, heat stabilizer, light stabilizer, flame retarder, lubricant, antistatic agent, rust preventing agent, fluorescent agent, surface smoothing agent, surface modifying agent, mold release agent and the like can be added. Particularly, for use as a injection molding material, it is preferred to add 30 to 40% by weight of fillers such as glass fibers, talc or the like based on the polymer in order to improve the elasticity or diminish anisotropy of molded parts.
It is preferred that the liquid crystalline polymer used in the invention has a ratio (viscosity 2)/(viscosity 1) of 0.10 to 0.70, more preferably 0.1 to 0.50, wherein(viscosity 1) is a melt viscosity under a shear rate of 1,000 secxe2x88x921 at a temperature at which an anisotropy melt phase begins (flow temperature) and (viscosity 2) is a melt viscosity measured under the same shear rate at a temperature higher by 20xc2x0 C. than the flow temperature. The flow temperature herein refers to a temperature at which a resin heated at a rate of 4xc2x0 C./minute shows a melt viscosity 48,000 poise when the resin is extruded from a nozzle having an inside diameter of 1 mm and a length of 10 mm under a load of 100 Kgf/cm2. The ratio of melt viscosity outside the above range is not preferred because, particularly when a film or a sheet is molded by extrusion molding, sometimes processability such as film winding property becomes inferior or anisotropy of the obtained product becomes large and thus the product can not be practically used.
It is preferred that, in the heat resistance, the liquid crystalline polyester resin used in the invention has a soldering heat resistance of 250xc2x0 C. or higher. The soldering heat resistance herein refers to the maximum temperature at which no blister or deformation is observed in a series of experiments in which a JIS 1(1/2) dumb-bell test piece having a thickness of 1.2 mm is molded, immersed in a solder bath at 240xc2x0 C. consisting of 60% of tin and 40% of lead, taken out after holding at the same temperature for 60 seconds and checked for outside appearance, and the procedure is repeated elevating every time the temperature of the solder bath by 10xc2x0 C. When the soldering heat resistance is lower than 250xc2x0 C., many limitations occur in use, for example, use of a part melt-bonded with a metal obtained in the invention in a solder reflow furnace.
It is preferred that the liquid crystalline polyester resin used in the invention has a melt tension of 10 g or more. The melt tension herein is an expression of a force charged on a tension pulley when a monofilament is broken in an experiment in which a resin is melted in a die of 8.0 mm (length)xc3x972.1 mm xcfx86 kept at a temperature 30xc2x0 C. higher than the flow temperature of said resin, extruded at a piston velocity of 2 mm/minute, taken off in the form of the monofilament with rollers after passing through the tension pulley and the taking off velocity is gradually increased. When the melt tension is lower than 10 g, processing for obtaining a molded article of the liquid crystalline polyester for use in the present invention sometimes becomes difficult due to insufficient elongation particularly in melt extrusion of a film or molding of a sheet.
Also, it is preferred that the intrinsic viscosity [xcex7] of the liquid crystalline polyester resin used in the invention is 5.5 or more. When [xcex7] is lower than 5.5, it is difficult to attain the above described melt viscosity characteristic and melt tension.
The liquid crystalline polymer obtained in this manner is treated and shaped by an injection molding machine or extrusion molding machine. Particularly, for the purpose of forming a substrate for circuit by melt-bonding with a metal, molded articles in the form of a film or sheet are preferred for handling and so on. More preferred is a film.
Particularly, examples of molding method for forming a film include the cast method in which a molten resin is extruded in a desired width and thickness from a slit-form machine called T-die and cooled as it is to form a film; the drawing method in which an extruded film is serially drawn in the machine direction and the crossing direction; and the film blowing method in which the resin is extruded in the cylindrical form from a circular die and blown simultaneously in the taking off direction and in the crossing direction by a gas. In the case of a liquid crystalline polymer, the blowing method is preferred because of easiness in controlling the anisotropy.
The process for melt-bonding the molded article of a thermotropic liquid crystalline polyester with a metal and the process for producing the molded article or laminated product according to the invention are described below.
The process for melt-bonding the molded article of a thermotropic liquid crystalline polyester with a metal is characterized in that it comprises activating a surface of a molded article of a thermotropic liquid crystalline polyester resin and melt-bonding said surface with a metal at or above the flow temperature of said thermotropic liquid crystalline polyester resin. The method for activating a surface of a molded article of a thermotropic liquid crystalline polyester resin includes previous irradiating with ultraviolet rays, corona discharge and plasma treatment. Particularly, it is preferred to irradiate a surface of a molded article of a thermotropic liquid crystalline polyester resin with ultraviolet rays containing a wavelength 254 nm.
The activated state of the surface of a liquid crystalline polyester resin includes a state where the resin surface oxidized, or a state where the functional group was formed by irradiation of ultraviolet rays, corona discharge or plasma treatment.
The oxidation degree of the resin surface is not limited especially, if the effect of the present invention is attained. For example, the oxygen atom in the element which constitutes the surface increases 5% or more, suitably 20% or more compared with the state before activation.
As the functional group formed in the surface, for example, hydroxyl group, a carbonyl group, etc. are exemplified, without being limited thereto.
Moreover, the density of the functional group is not limited especially, if the effect of the present invention can be attained.
Such activation is confirmed by measuring surface element composition with X-ray photoelectron spectroscopy. Moreover, when hydrophilic functional groups, such as a hydroxyl group and a carbonyl group, are formed in the surface, it is confirmed from lowering of the contact angle of water to the surface.
The molded article formed from a molded article of a thermotropic liquid crystalline polyester resin and a metal is obtained by applying the above described melt-bonding process. Particularly, a thin laminated product formed from a molded article of a thermotropic liquid crystalline polyester resin and a metal is obtained by applying the above described melt-bonding process to a thermotropic liquid crystalline polyester film or sheet and a metal. Hereinafter, the melt-bonding process is principally described but it is to be understood that the same process can be applied for the production of a molded article or a laminated product formed from a molded article of a thermotropic liquid crystalline polyester and a metal.
In the present invention, when the molded article of the thermotropic liquid crystalline polyester resin and a metal is melt-bonded, the temperature-for melt-bonding is preferably in a range of from the flow temperature plus 10 to 60xc2x0 C., more preferably plus 30 to 60xc2x0 C. When the temperature for melt-bonding is lower than the flow temperature plus 10xc2x0 C., sometimes the adhesive strength between the molded article and the metal is insufficient and when it is higher than the flow temperature plus 60xc2x0 C., sometimes deformation of the molded article becomes remarkable.
It is preferred that the surface roughness, expressed by Ra (average roughness along the central line), of the molded article of a thermotropic liquid crystalline polyester resin, obtained as described above, at a slide to be melt-bonded with a metal is in a range of from 1 to 50 xcexcm. Methods for adjusting the surface roughness at such value include, without limitation, a method in which the surface roughness of the mold cavity for use in the injection molding is adjusted to copy said roughness to the surface of the molded article; a method in which a film is continuously passed through a roll having embossment with compression and heating to copy said embossment; and a method in which a mold having embossment is pressed onto the molded article to copy the embossment.
The metal for melt-bonding with the molded article of a thermotropic liquid crystalline polyester resin used in the invention include copper, silver, gold, iron, zinc, magnesium, nickel and the like as well as alloy thereof. These may be an independent material or composite material. In addition, it can be a surface-treated metal, for example one treated with an aminosilane agent, insofar as the object of the invention is not prevented.
The form of the metal may be wires for forming an electric or an electronic circuit, or foils for forming a circuit by etching treatment, in addition to forms as structural parts. Particularly, for complex and fines circuit, a copper foil is preferred. When a copper foil is used, the foil is melt-bonded with a molded article of a thermotropic liquid crystalline polyester resin and then etched to form a circuit.
The copper foil, called electrolytic copper foil, generally has a thickness of 2 to 200 xcexcm, has fine copper particles deposited on a surface, coated with zinc or nickel and surface-treated. The present invention, however, is not limited to such foil.
Methods for melt-bonding the molded article of a thermotropic liquid crystalline polyester resin with a metal include a method in which the molded article and the metal are heated in a press machine set at the above described temperature for melt-bonding; a method in which the metal preheated to the above described temperature for melt-bonding is subjected to contact-bonding with the molded article; a method in which a molded article in the form of a film or a sheet and a metal foil are continuously compressed with hot rolls set at the above described temperature for melt-bonding and so on. In addition, each of the molded article and the metal may be adhered by one side or be adhered by both sides of one or both. Such manner is selected according to the shape required by desired parts.
In addition, it is possible to obtain a single melt-bonded molded article by a single melt-bonding operation from, for example, a molded article and a metal compressed with a press machine. Alternatively, it is also possible to obtain plurality of melt-bonded molded articles, separated between plurality of pairs of melt-bonded: metal and molded article with release film or the like by a single melt-bonding operation.